Stents are widely used for supporting a lumen structure in a patient's body. For example, stents may be used to maintain patency of a coronary artery, other blood vessels or other body lumen.
Stents are commonly metal, tubular structures. Stents are passed through a body lumen in a collapsed state. At the point of an obstruction or other deployment site in the body lumen, the stent is expanded to an expanded diameter to support the lumen at the deployment site.
In certain designs, stents are open-celled tubes that are expanded by inflatable balloons at the deployment site. This type of stent is often referred to as a “balloon expandable” stent. Other stents are so-called “self-expanding” stents. Self-expanding stents do not use balloons to cause the expansion of the stent. An example of a self-expanding stent is a tube (e.g., a coil tube or an open-celled tube) made of an elastically deformable material (e.g., a superelastic material such a nitinol). This type of stent is secured to a stent delivery device under tension in a collapsed state. At the deployment site, the stent is released so that internal tension within the stent causes the stent to self-expand to its enlarged diameter. Other self-expanding stents are made of so-called shape-memory metals. Such shape-memory stents experience a phase change at the elevated temperature of the human body. The phase change results in expansion from a collapsed state to an enlarged state.
A delivery technique for elastically deformable stents is to mount the collapsed stent on a distal end of a stent delivery system. Such a system would include an outer tubular member and an inner tubular member. The inner and outer tubular members are axially slideable relative to one another. The stent (in the collapsed state) is mounted surrounding the inner tubular member at its distal end. The outer tubular member (also called the outer sheath) surrounds the stent at the distal end.
Prior to advancing the stent delivery system through the body lumen, a guide wire is first passed through the body lumen to the deployment site. The inner tube of the delivery system is hollow throughout its length such that it can be advanced over the guide wire to the deployment site.
The combined structure (i.e., stent mounted on stent delivery system) is passed through the patient's lumen until the distal end of the delivery system arrives at the deployment site within the body lumen. The deployment system and/or the stent may include radiopaque markers to permit a physician to visualize positioning of the stent under fluoroscopy prior to deployment.
At the deployment site, the outer sheath is retracted to expose the stent. The exposed stent is now free to self-expand within the body lumen. Following expansion of the stent, the inner tube is free to pass through the stent such that the delivery system can be removed through the body lumen leaving the stent in place at the deployment site.
In prior art devices, the stent may prematurely deploy as the outer tube is retracted. Namely, with the outer tube partially retracted, the exposed portion of the stent may expand resulting in the remainder of the stent being squeezed out of the outer tube. This can result in the stent being propelled distally beyond a desired deployment site. Also, once the stent is partially unsheathed, it is sometimes determined that the stent placement needs to be adjusted. With existing systems, this is difficult since the stent has a tendency to force itself out of the sheath thereby making adjustments difficult. What is needed is a system that retains the stent on the catheter even when a majority of the stent has been exposed by retraction of the sheath, and allows a stent to be re-sheathed even after a majority of the stent has been exposed by retraction of the sheath.
Also, in existing systems, it is difficult to accurately determine the position of the stent. What is also needed is a system that provides an accurate visible indicator of the position of the stent.